Screw type apparatus for drying moist polymeric materials

ABSTRACT

The pressure and temperature and in some cases the flow rate of fluids such as polymers are controlled by reducing the cross-sectional area of the conduit carrying the fluid to provide a flow channel communicating with the inner surface of the conduit whose cross-sectional area is less than that of the conduit. A valve housing is provided containing a chamber which communicates with the flow channel. The pressure and temperature and in some cases the flow rate of the fluid is controlled by adjusting the position of a valve member slideably disposed in the chamber. As the valve member slides within the chamber, it enlarges or reduces the cross-sectional area of the flow channel to change the flow resistance of the channel, thereby changing the pressure and temperature upstream of the channel and in some cases the flow rate through the channel. 
     In applications where the material at the upstream end of the channel is wet and at a substantially greater pressure than the downstream end, it is desirable to also provide an elongated chamber whose inlet port communicates with the downstream end of the channel and which contains means for advancing and compacting material emanating from the downstream end of the channel. In cases where fragmentation of the material is produced by a rapid, and sometimes explosive, vaporization of the moisture associated therewith upon exposure of the material to the low pressure at the downstream end of the channel, the chamber contains the explosion, collects the resulting fragmented materials and compacts the fragments into a form more convenient to handle.

This is a division of application Ser. No. 217,744 filed Jan. 14, 1972,now abandoned.

BACKGROUND OF THE INVENTION

This invention relates broadly to an apparatus and method forcontrolling operation parameters such as the pressure, temperature andin some cases the flow rate of a fluid and, in particular, forcontrolling these parameters when the fluid is a polymer. Moreparticularly, the apparatus of this invention is a novel valve assembly,optionally modified with an extension on its downstream end forcollecting and compacting material emanating from the valve. The valveassembly has numerous uses and is particularly suitable for use inpolymer processing equipment in which the polymer is subjected toelevated temperatures and pressures. The valve assembly of thisinvention provides a means for quickly and conveniently accommodatingsuch equipment to changes in the capacity and operational parameterswhich become necessary from time to time. The valve assembly is alsoadvantageous in overcoming certain operational difficulties whichoccasionally affect such equipment.

A variety of equipment is available for processing polymeric materialsat elevated pressures and temperatures. For purposes of clarity andillustration only, the apparatus and method of this invention will bedescribed in connection with a single piece of processing equipment incommercial use at the present time. This equipment is commonly called an"Expanded-dryer" and is commercially available from ANDERSON IBEC,Strongsville, Ohio, the assignee of this application. The"Expander-dryer" is fully described in U.S. Pat. No. 3,222,797 (see inparticular FIGS. 1, 6-13 and the disclosure beginning in col. 7, line 36of the U.S. Pat. No. 3,222,797. The term "Expander-dryer" as used hereinmeans an apparatus of the type described in the U.S. Pat. No. 3,222,797.

The Expander-dryer has numerous uses but is particularly useful fordrying synthetic and natural rubber-like polymeric materials such asbutyl rubber, polybutadiene, polyisoprene, and the like. In suchmaterials, the amount of water in the finished product is a criticalproduction specification and ordinarily must be uniformly less than 0.5%and preferably less than 0.3%. Since many polymeric rubbers originallycontain substantial amounts of water, e.g., 50% or more, the materialmust be thoroughly dried at some stage during its processing. Thepolymeric materials are typically dewatered to a moisture content of 5to 20% using known equipment such as the Expeller press apparatus alsodescribed in the U.S. Pat. No. 3,222,797 and are then dried in theExpander-dryer to a product having less than about 0.5% moisture, usinga unique drying procedure.

The Expander-dryer comprises (1) a processing chamber having an inletand exit port, (2) means, such as a compaction worm assembly mounted ona rotatable shaft, for advancing the polymeric material through theprocessing chamber and for gradually building up the pressure within thechamber, (3) means for gradually increasing the temperature of thepolymeric material as it passes through the chamber and (4) dischargemeans such as a die plate disposed at one end of the chamber in order tomaintain suitable back-pressures in the processing chamber. As thepolymer advances through the processing chamber, the temperature andpressure are progressively increased. A unique feature of theExpander-dryer is that a sufficiently high pressure is maintained withinthe processing chamber to prevent the moisture associated with thepolymeric material from vaporizing within the chamber at thetemperatures present in the chamber. This is accomplished by preventingrelease of the pressure built-up within the chamber through thecooperation of the compaction worm assembly and the die plate.

As wet polymeric material is discharged from the processing chamberthrough the die plate, it enters a zone whose pressure is sufficientlylow to cause the hot liquid present in the polymeric material to rapidlyflash or vaporize. Some liquid is forcibly ejected from the polymer indroplet form at this point. The polymer and residual liquid containsufficient B.T.U.'s to flash substantially all the residual liquid tovapor in the low pressure zone. Escape of the vaporized liquid from thepolymer causes an expansion of the polymer to a porous structure (hencethe name "Expander-dryer") which permits the continued evaporation ofthe liquid until a substantially dry polymer is obtained.

The discharge die plate commonly used with such apparatus is ordinarilyan apertured plate with a fixed number of apertures and a fixed aperturesize. As a result, if, as is often the case, it becomes necessary toadjust the capacity or other operational parameters of theExpander-dryer beyond that for which the die configuration is suitable,the apparatus must be shut down and a suitable change made to obtain thedesired die configuration. This down-time can be costly and bothersome,and could be advantageously eliminated by a discharge plate whichpermitted the required adjustment of capacity or other operationalparameters of the apparatus while it continued in operation.

Moreover, as pressurized heated polymer is discharged from the apparatusinto the zone of reduced pressure, the moisture rapidly flashes tovapor, often with a violent and explosive force. In the case ofpolymers, such as styrene-butadiene and polybutadiene rubbers which haverelatively low tensile strengths and viscosities, there is a markedtendency for at least a portion of the polymer to fragment,disintegrate, or otherwise subdivide into very fine particles typicallyhaving a dimension of 0.5 millimeters, or less. These fragmentedmaterials are referred to in the art as "fines".

The "fines" present several problems. For example, they must becollected using hoods and other collection equipment to prevent unduecontamination of the atmosphere. In addition to the loss of polymercaused by the fines, they also have a tendency to coat the surfaces ofthe hoods and collection equipment where, upon standing for prolongedperiods of time, they degrade. The fines coating the inside surfacesalso tend to pick up moisture from the environment. Since the hoods andcollection equipment are necessarily in close proximity to the drieddischarged product, great care must be taken to insure that thesedegraded or moistened fines do not find their way back into the driedproduct to contaminate it with degraded or moist material. Isolatedspecks of wet fines in a product can result, for example, in a productwhose moisture content exceeds specification. A suitable means forsafely and conveniently recovering, collecting and converting the finesto a form in which they could be more easily handled would be mostadvantageous.

It is, therefore, a general object of this invention to provide a valveassembly and method whereby the pressure, temperature and in some cases,the flow rate of a fluid-like material such as a polymeric material, canbe quickly and conveniently adjusted and regulated without the necessityfor interrupting the flow of the fluid or for shutting down theequipment through which the fluid is flowing.

It is another object of this invention to provide an apparatus andmethod for collecting and reagglomerating into a useful form the finesproduced when a polymeric material is discharged from an Expander-dryer.

It is another object of this invention to provide an apparatus andmethod for preventing contamination of the dried polymeric productemanating from an Expander-dryer with degraded or moistened fines.

It is a further object of this invention to provide an apparatus andmethod for (1) controlling the pressure and temperature and in somecases also the capacity of an Expander-dryer without taking theequipment out of operation, (2) collecting and recovering finesdischarged from such an Expander-dryer before they can pick up moisture,or degrade and (3) reagglomerating these collected fines into a form inwhich they can be more conveniently handled and used.

It is a still further object of this invention to provide an apparatusand method for adjusting the capacity and operational parameters ofvarious types of known polymeric processing equipment such as extrudersand the like.

These and other objects of this invention will be apparent to oneskilled in the art from a total consideration of this disclosure.

SUMMARY OF THE INVENTION

The above objectives are obtained in accordance with the apparatus ofthis invention by providing a novel valve assembly for use inconjunction with polymeric processing equipment. In the valve assembly,flow restrictor means are disposed in the conduit through which a fluidis flowing to reduce the cross-sectional area of the conduit and providea channel between a surface of the restrictor means and a surface of theconduit. The cross-sectional area of the channel is less than that ofthe conduit. At least one valve housing is provided which contains achamber in communication with the channel. A valve member is slidablydisposed within the chamber. Means are supplied for adjusting theposition of the valve member within the chamber to thereby control thepressure and temperature and sometimes the rate of flow of material.Depending upon the position of the valve member in the chamber, thecross-sectional area of the channel can be increased or decreased toobtain the desired pressure and temperature upstream of the channel orin some cases the flow rate through the channel.

The valve assembly can be further provided with an elongated chamberhaving an inlet and exit port. The inlet end of the chamber communicateswith the downstream end of the conduit. This downstream chamber collectsfines discharged from the valve assembly in cases when the valveassembly is used in conjunction with an Expander-dryer which isprocessing a "fines producing" material. Means for compacting andadvancing the fines through the elongated chamber toward its exit portare also provided.

The downstream chamber is desirably free from any obstructions whichwould cause a substantial disparity (i.e. about 50 psi or more) to existbetween the pressure at the inlet port of the chamber and the dischargepoint of the downstream chamber during usage of the valve assembly. Thepressure of the discharge point is less than that of the materialupstream of the valve assembly, thus creating a low pressure zone in thevicinity of the inlet port of the chamber. When wet pressurizedpolymeric material is discharged from the downstream end of the valveassembly, it is discharged into this low pressure zone. The waterflashes to vapor and the vapor escapes by passing through the chamberand through the exit port of the chamber, without recondensing on driedpolymeric material flowing through the chamber.

If fines are to be reagglomerated by the compaction to which they aresubjected in the elongated chamber, it is desirable to create a slightback pressure (less than about 50 psi) in the chamber. This isconveniently accomplished by mounting a die plate across the exit portof the elongated chamber which contains at least one aperture. The totalcross-sectional area of all the apertures is sufficiently large,relative to that of the elongated chamber, that substantial pressuredifferences do not exist between the inlet and exit ports of thedownstream chamber during usage of the valve assembly.

In accordance with the method of this invention, the pressure,temperature and in some cases the rate of flow of a material through aconduit is adjusted by providing in the conduit an obstruction forreducing the cross-sectional area of the conduit. The obstructioncreates a channel between a surface of the obstruction and an innersurface of the conduit which has a cross-sectional area less than theconduit. The cross-sectional area of at least a portion of this channelis then increased to provide in said channel an enlarged portion towhich material flowing through the channel has access.

The pressure and temperature upstream of the channel and sometimes therate of flow of material through the channel are controlled by adjustingthe cross-sectional area of the channel to alter the flow resistance ofthe channel as desired.

The apparatus and method of this invention are described in greaterdetail hereinbelow, in conjunction with the description of the preferredembodiments shown in the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a partial side sectional view of the valve assembly of thisinvention (shown on the left side of FIG. 1A) used in conjunction with aprior art Expander-dryer (a portion of which is shown on the right sideof FIG. 1A). A vertical dividing line L--L separates the prior artapparatus from that of this invention.

FIG. 1B is a side view, partly in section and partly in schematic, whichis an extension from the right side of FIG. 1A and which showsadditional structure of the prior art Expander-dryer.

FIG. 2 is a view, partly in section, taken generally along the line 2--2of FIG. 1A and shows the valve assembly in its closed position.

FIG. 3 is a view, partly in section, taken generally along the line 3--3of FIG. 1A and shows the valve assembly in the same closed position ofFIG. 2.

FIG. 4 is a view identical to FIG. 2 except that it shows the valveassembly in an open position.

FIG. 5 is a view identical to FIG. 3 except it shows the valve assemblyin an open position.

FIG. 6 is a modified embodiment of the apparatus of the inventionsimilar to that shown in FIG. 1A with the compaction worm assembly onthe left side of FIG 1A omitted.

FIG. 7 is a view of a fragmentary portion of the apparatus of FIG. 1Aand illustrates means for attaching the apparatus of this invention toexisting equipment not provided with same.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

For illustrative purposes only, the apparatus of this invention is shownin use with the prior art Expander-dryer discussed hereinabove. Althoughsome structure of the Expander-dryer must necessarily be shown, thereader is referred to U.S. Pat. No. 3,222,797 for a more detaileddescription of the Expander-dryer. The Expander-dryer is shown in FIG.1B and in the right side of FIG. 1A which, for greatest clarity, shouldbe placed side by side as indicated. Referring to FIGS. 1A and 1B, theExpander-dryer comprises an elongated cylindrical housing 10 containinga cylindrical conduit 10a in which is disposed a rotatable shaft 11. Acompaction worm assembly comprising a plurality of worms 12 is removablymounted on shaft 11 by worm collar 12a (which is integral with worms 12)and key 12b, which fits into a keyway formed by cooperating axialgrooves in the outer surface of shaft 11 and the inner surface of collar12a (in a manner similar to that shown in FIGS. 2 and 4 and discussed indetail hereinbelow). Collar 12a is restrained from axial movement alongshaft 11 by a shaft cap 80 (see FIG. 1A) discussed in greater detailhereinbelow. Shaft 11 is supported at one end by bearing structure 13and rotatably driven by motor assembly 14, both shown schematically inFIG. 1B. Housing 10 comprises outer and inner annular metallic walls 15and 16, respectively. Housing 10 is not vented so that pressure built upin conduit 10a is not released.

In operation, a rubbery polymeric material containing from about 5 to20% water is fed to the Expander-dryer from a hopper through inlet chute17 (FIG. 1B). The polymeric material is advanced into the conduit 10a bythe rotating feed worms 12. As the material advances through the conduit10a, it is compacted as a result of the gradually decreasing pitch ofworms 12. The compacting action progressively increases the pressure inconduit 10a as the polymer advances through the apparatus. As thepolymer enters conduit 10a, it is subjected to heated inner wall 16 andits temperature progressively increased as it proceeds through conduit10a. Heat is supplied to wall 16 by any conventional means such as, forexample, a steam jacket or high resistance electrical wiring (notshown).

Conduit 10a is provided with a plurality of breaker bolts 18, whichextend into conduit 10a and are shown disposed on the top and bottom ofhousing 10 approximately 180° apart. Breaker bolts 18 are mounted in abar 19 which is affixed to the outer surface of housing 10. The breakerbolts prevent the polymer from rotating with the worms 12 and collar 12aand increase the compaction of the polymer. The pressure in conduit 10ais maintained at a value which will insure that the moisture associatedwith the polymer remains in its liquid state. To cause the desiredpressure build-up in conduit 10a, it is necessary to provide at the exitport 20 means for creating a back pressure in conduit 10a. Previously,this was ordinarily accomplished by the use of an apertured die plate asheretofore discussed. The valve assembly of this invention represents animproved means for creating the required back pressure and can beadvantageously used to replace the die plate designated by numeral 79 inFIG. 6a of U.S. Pat. No. 3,222,797.

The valve assembly 21 of this invention (see the left side of FIG. 1A)is provided with an upstream flange 22 disposed adjacent the exit port20 of the Expander-dryer and is mounted to a downstream flange 23 of theExpander-dryer by bolts 24, as shown in FIG. 1A. Valve assembly 21comprises a conduit 25 of substantially the same dimension as theconduit 10a of housing 10. Conduit 25 communicates at its upstream end25a with the exit port 20 of the Expander-dryer. Conduit 25 is definedby outer and inner walls 26, 27 similar to outer and inner walls 15 and16 of the Expander-Dryer.

Disposed within conduit 25 is a rotatable shaft 28 which cooperates withshaft 11 in such manner that shafts 28 and 11 rotate in unison. Thiscooperation can be achieved by making shaft 28 integral with shaft 11 asshown in FIG. 1A, or by coupling or otherwise affixing shaft 28 at itsupstream end to the adjoining downstream end of a pre-existing shaft 11.One such technique for coupling the shafts together is shown in FIG. 7.

Referring to FIG. 7, it is seen that the end of shaft 11 contains athreaded female recess 29 into which is threaded the male extension 30of the upstream end of the shaft 28. The direction of the threads issuch that when shaft 11 rotates, the connection between the two shaftsis tightened. If the valve assembly 21 is to be installed on apre-existing Expander-dryer, shaft 28 is conveniently coupled to the endof shaft 11 as shown in FIG. 7. In the case of newly manufacturedequipment, a similar arrangement can be used or a single integral shaft,as shown in FIG. 1A, can be provided throughout the entire length of theExpander-Dryer and the valve assembly 21.

Returning to FIG. 1A, the cross-sectional area of conduit 25 is reducedby the obstruction 32 mounted on shaft 28. As best shown in FIGS. 1A, 3and 5, obstruction 32 comprises (i) a central cylindrical member 33whose axis substantially coincides with that of cylindrical conduit 25and (ii) two edge portions 34, 34a, which are integral with member 33and conically taper toward the axis of member 33. As shown in FIGS. 2and 4, obstruction 32 is collar mounted on shaft 28 by a key 31 whichfits into the keyway defined by groove 32a of obstruction 32 andcooperating longitudinal surface groove 28a of shaft 28. Portions 34 and34a narrow into a cylindrical collar 39 which fits over shaft 28.Obstruction 32 is rotatable about its axis but is restrained from anylongitudinal movement along its axis by shaft cap 80 (FIG. 1A), asdiscussed in more detail hereinbelow. Obstruction 32 is removablymounted on shaft 28 in order to permit rapid and convenient replacementby constructions of varying geometries.

Cylindrical member 33 creates a thin annular channel 35 between itsouter peripheral surface and the inner surface 36 of wall 27. Thecross-sectional area of channel 35 is less than that of thecross-sectional area of conduit 25. The thickness of annular channel 35can vary considerably but is preferably substantially less than that ofthe radius of conduit 25. In one preferred embodiment, its thickness isabout 1/32 of an inch.

As heated pressurized polymer is discharged from the exit port 20 of theExpander-dryer and into conduit 25 of valve assembly 21, it is deflectedby the upstream conical portion 34 of obstruction 32 into the upstreamend of annular channel 35 (see FIG. 1A). The polymer passes throughchannel 35, emerging at the downstream end of channel 35, and thereuponexpands past downstream conical portion 34a back into conduit 25. It isthus seen that at least a portion of shaft 28, as represented byobstruction 32, has a cross-sectional area larger than that of theremainder of the shaft and that this enlarged portion of shaft 28creates a flow channel 35 which communicates with the inner surface 36of conduit 25.

A pressure gauge breaker screw (not shown) can be provided to facilitatethe measurement of the pressure at the upstream end 25a to conduit 25.

As best seen in FIGS. 2 to 5, two valve housings 40, disposed at anangle of approximately 180° apart from each other are externally mountedon valve assembly 21. Housing 40 contains a chamber 41 in which a valvemember 42 is slidably disposed. Aligned apertures 43 are provided inconduit walls 26 and 27 so as to provide communication between flowchannel 35 and chamber 41 of the valve housing 40. Apertures 43 aresized to accommodate passage of valve member 42. Housing 40 is mountedto upstream flange 22 by bolts 45.

Valve member 42 contains a recess 46 which is adapted to receive the endplug 47 of threaded cylindrical valve control rod 48. Rod 48 contains anarrowed neck portion 49, one end of which is attached to end plug 47. Asplit ring collar 50 envelops neck portion 49 and is affixed to theadjacent surface 42a of valve member 42 by screws 51. Surface 42a ofvalve member 42 contains a peripheral groove 42b in which is disposed asealing gasket 42c. The surface 88 of valve member 42 which communicateswith channel 35 is slightly curved so that in the closed position itwill be substantially flush with the inner surface 36 of conduit 25.

A valve rod retainer plate 52 is affixed to a surface of the valvehousing 40 by screws 54. Plate 52 contains a threaded chamber 53 whichcommunicates with chamber 41 and which is designed to accommodate rod48. Rod 48 is threaded to cooperate with the threads provided in chamber53. As rod 48 is rotated in one direction, it is withdrawn from plate 52simultaneously retracting valve member 42 through chamber 41 to therebyopen the valve. As rod 48 is rotated in the opposite direction, valvemember 42 is caused to reverse direction in chamber 41 and advance inthe direction of channel 35 to close the valve. A scale 55 is mounted onbracket 56 and serves to accurately control the degree to which thevalve is opened or closed.

FIGS. 2 and 3 show the valve in its fully closed position. In thisposition, valve member 42 does not enter channel 35 (see FIG. 2). Thus,some degree of flow can occur through channel 35 even when the valve isin the closed position. Valve member 42 is prevented from enteringchannel 35 by the enlarged section 58 of valve control rod 48 whichseats in the annular bevel 60a of plate 52 as rod 48 is rotated to closethe valve. Since the enlarged end 58 of control rod 48 is too large topass through chamber 53 of plate 52, movement of valve member 42 ceaseswhen portion 58 reaches bevel 60a. The enlarged end 58 is spaced on rod48 to insure that valve member 42 stops when the curved surface 88 ofvalve member 42 is substantially flush with the inner surface 36 ofconduit 25.

FIGS. 4 and 5 show the valve in an opened position. Referring to theseFigures, it is seen that by retracting valve members 42 thecross-sectional area of at least a portion of channel 35 is enlargedradially outward from the axis of conduit 25 to provide an enlargedportion of channel 35 to which material flowing through channel 35 hasaccess. The enlarged portion comprises the chamber defined by theapertures 43 in inner and outer walls 27, 26 and that portion of chamber41 which communicates with apertures 43. As shown in FIGS. 4 and 5,member 42 has not been fully retracted so that the enlarged portion ofchannel 35 comprises only apertures 43. Were member 42 to be furtherwithdrawn, it is apparent that the enlarged portion of channel 35 wouldbe even further increased to include a portion of chamber 41.

It can be seen that the cross-sectional area of channel 35 is adjustedsolely by adjusting the volume of this enlarged portion. The volume ofthe enlarged portion will vary depending upon the extent to which valvemember 42 has been withdrawn. As valve member 42 is withdrawn, polymericmaterial flowing through channel 35 will have access to the enlargedportion created thereby thus, in effect, increasing the cross-sectionalarea of channel 35 to reduce the flow resistance offered by the valve aslong as valve member 42 is withdrawn. As valve member 42 is urged towardchannel 35, polymeric material present in chamber 41 and apertures 43 isexpelled into channel 35 and the enlarged cross section of channel 35 isreduced, thereby increasing the flow resistance offered by the valve.

Although valve member 42 is prevented from entering channel 35 in thepreferred embodiment shown in the drawings, it will be apparent that thevalve assembly could be readily modified to allow valve member 42 toprotrude into channel 35 for as great a distance as desired. Thus, thelength of the threaded portion of rod 48 could be extended by reducingthe length of portion 58 to thereby allow valve member 42 to extendfurther into channel 35. In the case where valve member 42 does extendinto channel 35, the enlarged portion of said channel referred tohereinabove comprises the channel itself, apertures 43 and the portionof chamber 41 which communicates with apertures 43.

It is thus seen that the valve structure of this invention allows theflow resistance in polymeric processing equipment to be adjusted inorder to accommodate the equipment to an adjusted capacity or adjustedoperational parameters such as upstream temperature or pressure withoutthe need for discontinuing the use of the equipment or halting the flowof polymer through the equipment. It is apparent that thecross-sectional area of channel 35 can be widely varied depending uponthe dimensions of valve member 42 and the extent to which member 42 iswithdrawn. In designing the valve assembly, accommodations can be madeto provide the desired range of flow rates and operational parameterswhich are foreseeable for the piece of equipment with which the valve isto be used. The valve will remain permanently mounted on the equipmentand changes in capacity or operational parameters can be quickly andconveniently accommodated by simply adjusting the cross-sectional areaof channel 35 to the appropriate degree.

When the valve assembly is used in conjunction with an Expander-dryer,it is, on occasion, desirable to further provide an elongated chamberwhich communicates with the downstream end of channel 35. This chamberwill contain the fines produced by the explosive forces generated whenthe polymer emerges from channel 35 into the low pressure zone andprevents them from scattering. By including within the chamber a meansfor compacting and advancing the fines through the chamber, the finesare reagglomerated and discharged in a useful form.

To this end, there is shown in FIG. 1A an elongated cylindrical chamber60, which contains a conduit 61 which is in communication with equaldimensioned conduit 25 of valve assembly 21. As shown in FIG. 1A, valveassembly 21 and elongated chamber 60 appear as an integral unit. Incases where fines are not a problem, the elongated chamber is notrequired and the valve assembly 21 is provided as a separate unitconnected at its upstream end to the Expander-dryer as shown in FIG. 6.In FIG. 6, valve assembly 21 is provided with a downstream flange 59. Ifdesired, an elongated chamber 60 can be provided with an upstream flangefor coupling to flange 59 in cases where fines are a problem. For thiscontingency, shaft 28 is also provided with a removable cap 80 similarto that shown in FIG. 1A which is threaded into the recess 28c at theend of shaft 28.

Thus, valve assembly 21 and elongated chamber 60 can be integral orseparated as desired. The ensuing description is with reference to FIG.1A in which the valve assembly 21 and chamber 60 are integral. Althoughvalve assembly 21 and chamber 60 share in common a number of featuressuch as the central conduit and the conduit walls, the common featureshave been separately numbered to maintain a distinction between thevalve assembly 21 and chamber 60 since, in certain cases, they could beseparable from each other along vertical line X-X of FIG. 1A and asindicated by FIG. 6.

Referring to FIG. 1A, it is seen that conduit 61 contains disposedtherein a rotatable shaft 62 on which is collar mounted a compactionworm assembly (similar to worm assembly 12 on the right side of FIG. 1A)comprising a plurality of compaction worms 63. The worm collar 63a ismounted on shaft 62 by a key-keyway arrangement 63b identical to thatshown in FIGS. 2 and 4. Preferably, the pitch of worms 63 progressivelydecreases as the worms approach the exit port 64 of conduit 61. Conduit61 is provided with inner and outer walls 65, 66, similar to walls 26,27 and 15, 16. Chamber 60 also contains a plurality of breaker bolts 67mounted in breaker bolt bar 68. The breaker bolts are disposed in anupper and lower row spaced approximately 180° apart. Two or more rowscould be added if desired to create four rows 90° apart. Worms 63 extendonly about 3/4ths of the way around the periphery of shaft 62 so as tonot contact breaker bolts 67 as shaft 62 rotates. Breaker bolts 67 servethe same function as the breaker bolts 18 of the Expander-dryer.

As shown in FIG. 1A, shaft 62 is integral with shaft 28 and rotates inunison with shaft 28 in response to the rotation of shaft 11. If chamber60 were a separate unit, shaft 62 could be coupled or otherwise fixed atone end to the adjoining end of shaft 28 in a manner similar to thatshown in FIG. 7.

Worm assemblies 63 and 12, as well as obstruction 32 are restrained fromlongitudinal movement along shafts 62, 11 and 28, respectively, by shaftcap 80. Cap 80 is a cylindrical member whose outside diameter isapproximately the same as that of the collars of worm assemblies 63 and20. It is held in place at the end of shaft 62 by a threaded maleprojection 81 which cooperates with the threaded recess 82 in thesurface 83 of shaft 62.

Conduit 61 is free from any obstructions which would cause a substantialdisparity to exist between the pressure at its inlet port 69 anddischarge port 64. The reason for this is that the hot pressurizedpolymeric material must emanate from the downstream end of channel 35into a zone which is maintained at a sufficiently low pressure to allowthe liquid associated with the polymer to rapidly flash into vapor.Since inlet port 69 communicates with the low pressure atmospherenormally surrounding the equipment (through conduit 61 and, whendischarge plate 70 is used, through apertures 71 in plate 70), thepressure at exit port 69 should be substantially the same as that atexit port 64. (In this regard, chamber 60 could also be provided withventilation apertures or slots.) Polymer discharged from channel 35 thenloses its moisture by evaporation and the evaporated moisture passesdown conduit 61 and discharges to the atmosphere. If, for any reason,the pressure at inlet port 69 was sufficiently high to prevent moisturein the polymer discharged from channel 35 from vaporizing, effectivedrying of the polymer would not be obtained. Moreover, even if themoisture was vaporized, the possibility would exist that the moisturecould condense back onto the polymer in conduit 61 if excessively highpressures were present at any point in conduit 61. To preclude theseundesirable effects, it is preferable that the pressure at the inlet andexit ports 64, 69 of conduit 61 not vary substantially and that thepressure at inlet port 69 be sufficiently low to permit vaporization ofthe liquid carried by the polymer.

As the polymer emanates from channel 35, the normal product and anyfines generated by this explosive vaporization of liquid are confinedand collected by conduit 61 and are transported from the inlet port 69of conduit 61 to the exit port 64 by compaction worms 63. Worms 63 exerta mild compacting pressure on the fines which reagglomerates the finesinto an easier to handle form. It has been found that a small amount ofback pressure is desirable in conduit 61 to assist in the agglomerationof the fines. For this purpose, a discharge plate 70 can be optionallyattached to downstream flange 84 across exit port 64 of conduit 61 bybolts 85. Generally, plate 70 contains one or more apertures 71;however, the total cross-sectional area of the apertures must besufficiently large, relative to that of conduit 61, that substantialpressure differences do not exist between the inlet and exit ports ofconduit 61 during usage. Generally, the elongated chamber 60 of thisinvention is designed so that exit port 64 communicates with anenvironment which is either at atmospheric or subatmospheric pressure,and wherein the pressures present in conduit 61 during operation areless than about 50 p.s.i. and preferably within the range of from about10-50 p.s.i.

The specific embodiments, drawings and detailed descriptions presentedhereinabove are illustrative only and such alterations and modificationsthereof as would be suggested to one skilled in the art are deemed tofall within the scope and spirit of the claims appended hereto.

I claim:
 1. In an apparatus for drying moist polymeric materialincluding (a) a processing chamber having an inlet port and an exitport, (b) a compaction worm mounted on a first rotatable shaft disposedwithin said processing chamber for advancing material to be dried fromthe inlet port to the exit port while progressively compacting andthereby increasing the pressure of the material as it advances, (c)means for gradually increasing the temperature of the material as itadvances through said chamber, the pressure developed due to compactionof the material being sufficient to substantially prevent vaporizationof the moisture associated with the material in said processing chamber,and (d) discharge means associated with the exit port for maintaining asuitable back-pressure in said processing chamber and for releasing thematerial to a relatively low pressure environment as compared to thepressure developed in said processing chamber, the improvement in saiddischarge means comprising:1. a cylindrical conduit having an inlet portand an exit port, the inlet port of said conduit communicating with theexit port of said processing chamber;
 2. a second rotatable cylindricalshaft mounted concentrically in said conduit and connected to said firstshaft for rotation in unison therewith, said second shaft havingdiameter substantially less than the inside diameter of said conduit; 3.valve means associated with an intermediate portion of said conduit forproviding a passageway of controllable cross-sectional area from theportion of said conduit upstream of said valve means to the portion ofsaid conduit downstream of said valve means including:3a. an obstructionmounted on said second shaft, said obstruction having a smoothcylindrical outer surface concentric with said second shaft, thediameter of said obstruction being substantially greater than thediameter of said second shaft but less than the inside diameter of saidconduit; 3b. at least one valve housing mounted externally of saidconduit and containing a valve chamber continuously communicating withthe interior of said conduit from a region upstream of said obstructionto a region downstream of said obstruction; 3c. a valve member slidablydisposed in said valve chamber for radial motion with respect to saidconduit for controlling the volume of said valve chamber communicatingwith said conduit to control the cross-sectional area of saidpassageway; and 3d. means associated with said valve member forcontrolling the position of said valve member in said valve chamber; and4. means associated with the portion of said conduit downstream of saidvalve means for releasing the material exiting from said passageway tosaid relatively low pressure environment within said downstream portionof said conduit to permit substantially all of the moisture associatedwith the material exiting from the passageway to immediately vaporizeand immediately expand the material to the full extent required for saidvaporization, thereby drying the material, and for compacting andadvancing the dried material to the exit port of said conduit underpressures sufficiently low to prevent substantial recondensation of thevapor on the dried material including:4a. a plurality of worms spacedlongitudinally on said second shaft downstream of said obstruction toform an interrupted compaction worm flight for advancing the driedmaterial to the exit port of said conduit and progressively compactingthe dried material as it advances without creating a substantialpressure difference between the exit port of said conduit and thedownstream end of said passageway during compaction and advance of thematerial; and 4b. a plurality of breakers mounted on said conduit andprojecting into the interior of said conduit intermediate at least someof said worms to prevent the dried material from rotating with theworms.
 2. The apparatus defined in claim 1 further comprising meansassociated with said valve member for preventing the valve member fromextending from said valve chamber into the interior of said conduit. 3.The apparatus defined in claim 1 further comprising:5. a plate mountedacross the exit port of said conduit, said plate containing at least oneaperture, the total cross-sectional area of said aperture beingsufficiently large relative to that of said conduit so that substantialpressure differences do not exist between the exit port of said conduitand the downstream end of said passageway.
 4. The apparatus defined inclaim 1 wherein the vapor exits from said conduit via the exit port ofsaid conduit.